Airsick is, to borrow a phrase from football commentators, a play of two halves. Billed as a black comedy, its comedy is confined largely to its first half while its blackness is all bundled up in the second - which makes the whole of this stage debut from screenwriter Emma Frost, while intriguing, rather less than the sum of its uneven parts.

Set in post-911 London, Airsick centres around best friends Lucy and Scarlet and the men in their lives. Scarlet's men are mainly faceless. Lucy's are three-strong - her world-weary father Mick, her American ex-pat boyfriend Joe and her secretive admirer, a Kiwi globetrotter named Gabriel. These men and the women are, to varying degrees, all sexual predators and emotional pygmies, seemingly intent on proving Mick's maxim that we really are better off alone.

Frost proves a dab hand at dialogue, particularly in the more light-hearted first half, where in addition to some wry and flirtatious banter, there's a skilfully and amusingly orchestrated dinner party scene. Her second half becomes increasingly reliant on flurries of long and short monologues which, while often poignant, suffer from overuse.

Bush artistic director Mike Bradwell gives Frost's first play a slick premiere production, with big brownie points owing to Es Devlin's black Perspex set that, behind its many reflective panels, hides cupboards, fridges, phones, projections and a hydraulic lift that multi-tasks as table, bed, sofa and more.

Castwise, Celia Robertson's physical proportions may be less ample than Lucy seems to require, but she doesn't skimp elsewhere with her genuinely moving portrait of a young woman worn down by others' demands of her. And, in their different ways, both Peter Jonfield as Mick and Susannah Doyle as Scarlet tread a fine line between hard-bitten though never heartless.

Though Eric Loren and Gideon Turner (as Joe and Gabriel) turn in capable performances that are, respectively, boorish and mysterious as required, Frost's script is less kind to these two. As proceedings take a turn and at least three alternative endings fly past - in filmic terms: a) romantic comedy, b) sentimental weepie, and c) murder mystery - the final analysis of both men veers from caricatured to slightly ludicrous, and neither the least bit flattering.

Frost's efforts to hammer home black hole theory, in sometimes crudely anatomical fashion, is a metaphor too far. The title, and Lucy's own abject fear of flying, do quite nicely in conveying the turbulence inherent in life's journey. So, too, for the play itself. A bit of a rough ride, it may leave you queasy for longer than you expect. But that's not necessarily a bad thing.

- Terri Paddock